Purity (D2 standard libraries / object.d)

[Andrei Alexandrescu]

Walter Bright wrote:
> Jason House wrote:
>> Walter Bright Wrote:
>>
>>> Jason House wrote:
>>>> When considering the standard library changes, I realized that 
>>>> object.d could change. I believe a pure opCmp or toString could
>>>> break user code with impure versions of those functions. Would
>>>> that kind of a change to object.d cause any real problems for D2
>>>> users?
>>> As Andrei pointed out, the trouble with making the Object functions
>>> pure is if you want to do an override that caches its value.
>>
>> One could easily generalize that to mean non-final virtual functions
>> should never be pure. Memoizaton is a pretty basic need. I thought
>> that was in D's future. Is that not true?
> 
> Memoization and purity don't mix. For each function, you'll have to pick 
> which way you want to go. I don't see what that has to do with D's 
> future, though, the language allows either.

Memoization and purity can and should go together. We need to sit down 
and discuss that someday.

Andrei